Here it is in a nutshell – and I agree completely.
…many Christians have a VERY negative view of the human condition. They typically think that as human beings we are deeply flawed or incapable of making reasonable and rational decisions. The doctrine of original sin, proposed in the fourth century of the Common Era by Saint Augustine is partly to blame. Augustine (who was African) had many personal struggles with his humanity, including a tremendous guilt for his sexual practices, and, consequently, he concluded that the human condition was “depraved” or corrupt from birth. As the Church continued to institutionalize, first as the Catholic Church, it also continued to incorporate Augustine’s theory of original sin into the systematic development of Christian theology. All over the world this theory dominates Christian thinking and practices to the extent that many contemporary Christians, both Catholic and Protestant, demonstrate that they believe like Augustine: that it is impossible for us as humans to be good or moral without supernatural help.
Hat tip to PZMyers